Polybutadiene, modified polybutadiene, method for producing both, and rubber-reinforced styrene resin composition using same

A polybutadiene characterized in that (1) content of 1,2-structure in the polybutadiene is 4 to 30%, (2) content of cis-1,4-structure in the polybutadiene is 65 to 95%, and (3) content of trans-1,4-structure in the polybutadiene is 5% or less, a ratio (Tcp/ML1+4) of a 5% toluene solution viscosity (Tcp) measured at 25° C. and a Mooney viscosity (ML1+4) at 100° C. is 2.0 or higher, a molecular weight distribution (Mw/Mn) is 2.80 or less, a gel content is 0.06 wt % or less, and an APHA color is 20 or less,

• wherein the polybutadiene is a product produced by a polymerization process in which a polymerization inhibitor is added to a polybutadiene solution, thereby to stop a polymerization in a stirring state where polymerization inhibitor particles each having a particle size of 135 mm or less are dispersed in the polybutadiene solution.